The present invention relates to a joint having a small diameter and in particular to a universal joint having a high durability, which couples two dynamic force transmitting shafts deviated slightly in an angular direction from each other.
FIGS. 7(a) and 7(b) show a bending joint 700 made of a light alloy by mechanical processing in one body, having a small diameter and suitable for dynamic force transmission; FIG. 7(a) being a side view shown in a direction perpendicular to an axis line, FIG. 7(b) being a side view shown parallelly to the axis line. A first slit 702 is formed, which traverses an axis line S in a cylinder cutting direction perpendicular to the axis line S, starting from a cylindrical surface 701, leaving a part exterior to a chord C forming a center angle of about 90xc2x0 C. Then a second slit 703 is formed similarly and parallelly to the first slit 702 in a reverse direction at a position separated from the first slit 702 by a small distance d along the axis line S, the slits forming a pair.
Further a third and a fourth slit 704 and 705 forming another pair are formed in an orthogonal direction with respect to the pair formed by the first and the second slit 702 and 703 at a position separated from the second slit 703 by the same distance d similarly to the pair formed by the first and the second slit 702 and 703. Still further a pattern of the first slit 702 to the fourth slit 705 is repeated with the same separation distance d from the fourth slit 705. By forming such slits 702 to 705 in series, even if a mounting axis line Se of a driven shaft 712 is deviated with respect to a driving shaft 710, deviation can be absorbed by variations of widths xcex4of the slits 702 to 705 and it is possible to deal therewith flexibly for transmitting rotation between the different axis lines.
Such a bending joint 700 is less flexible than a bending joint, in which a slit is formed in spiral and it has a smaller region of angular deviation between axis lines to be connected. However, since it can deal therewith for either rotational direction, forward or reverse, it has a high mechanical strength, and rotation transmission precision increases with increasing dynamic force transmitting torque, it is excellent in safety, reliability and durability.
However formation of the first slit 702 to the fourth slit 705 includes a number of fabrication steps and it is difficult to expect so as to have a high processing precision. Even if the processing is automated, since one cannot help relying on mechanical cutting processing, equipment investigation and production cost cannot be reduced. Further, since it is formed in one body, it is poor in adaptability, in case where dynamic force transmitting shafts having different diameters should be coupled. Further, since the different slits 702 to 705 traverse the axis line S of the bending joint 700, transmitted torque is absorbed by center displacement due to twisting deformation of linking parts 706 and according to measurements a relationship between rotation angle and torque cannot be represented not by a smooth curve but by a waveform. This is a problem, to which attention should be paid, particularly when it is applied to a mechanism such as an encoder, etc., to which precise angle transmission is necessary.
Moreover a universal joint disclosed in Japanese Utility Model Publication No. Hei 7-52428(B) solves the problem and contributes to not expensive supply thereof, because mass- production is possible therefor. However external shape thereof is somewhat complicated and one cannot help relying on manual work for linkage of two members by means of screws at mounting. Moreover, since throughholes required for making; screws pass through are formed in the neighborhood of a hole for the dynamic force transmitting shafts, thickness of parts linked by means of screws, to which load to be transmitted is applied, is reduced, which causes decrease in mechanical strength, and durability decreases due to variations in stress during rotation given repeatedly to the throughholes. Since a certain thickness remaining after formation of the throughholes is necessary, down-sizing for the purpose of space saving is limited even at the sacrifice of mechanical strength and it is unsuitable for a universal joint having an outer diameter smaller than 20 mm.
An object of the invention is to provide a universal joint at a low cost, which can deal with a great torque to be transmitted not at the sacrifice of strength and suitable for a coupling having a small diameter producing no errors of rotational angle transmission and having a high precision as well as a high durability.
In order to achieve the above object a universal joint according to the present invention having a bending coupling structure comprises a pair of thin bending plates, each of which has a basic shape of a ring; a pair of linking boss portions, each of which supports deformably one of the thin bending plates at two points in the neighborhood of two extremities of a diameter on a one-side surface thereof; and an intermediate disk supporting the thin bending plates similarly at two points on each surface in the neighborhood of two extremities of a straight line orthogonal to the diameter.
The linking boss portions and the intermediate disk are made of a high duty aluminium alloy for elongation having a high tenacity or other equivalent materials by die cast and a round plain arbor for caulking protruding from the center of each of supports holding the thin bending plates, which secures directly one of the bending plates, is formed in one body therewith.
The high duty aluminium alloy is an Al-Mg-Cr alloy (hydronarium or hydro) and each of the bending plates is a thin plate, whose thickness is smaller than 0.6 mm, made of glass fiber reinforced polyimide or another equivalent synthetic resin. Further the bending plate may be a thin plate made of carbon fiber reinforced epoxy resin or another equivalent resin, whose thickness is smaller than 0.8 mm.
Moreover it is preferable to form the bending plate by superposing a stainless steel thin plate having a same shape, whose thickness is smaller than 0.4 mm, on the synthetic resin thin plate. In addition, the round plain protruding arbor for caulking may be constructed in one body by insert formation using another suitable member at the die cast formation of each of the linking boss portions and the intermediate disk.